The invention relates to a separating unit for flat sheet material having a separating drum, able to be turned and which in its outer face has suction openings, and in which, in operation, the furthest forward piece of sheet material to be separated is run tangentially to the separating drum through a gap formed between the separating drum and a suction drum turning in the same direction, the sheet material being suction-gripped by way of suction openings on the outer face of the separating drum and being run into a transport system.
In the present case "flat sheet material" is to be taken to be, more specially, banknotes, bankpapers, data or other records and pages of papers with printed material or handwriting.
An account is given of a separating unit for flat sheet material in the German Offenlegungsschrift Specification No. 2,454,082, in which the piece of sheet material furthest to the front of a stack of material being transported is guided by way of a turning suction drum, which is placed, as seen in the direction of motion, at the back end of the stack, and by way of a shaker into a gap or slot, which is formed by a second turning suction drum and a still further turning suction drum, acting as a separating drum, and the separating drum and the second suction drum, the "keeping-back drum", are turned in the same direction. The second suction drum is responsible for keeping back or pushing back all that flat sheet material, which comes after the furthest-forward sheet of material, that is to say the piece of sheet material which is to the front. As a general rule, the leading edge of the sheet material to be separated is kept up against the keeping back roller till the suction openings, which, in comparison with the suction openings of the keeping back roller, have a very much greater suction force, of the separating roller take over the sheet material, so that it is pulled from the stack and handed over to the next part of the transport system. With this apparatus, a high-speed and trouble-free separating of flat sheet material is possible.
However, it is more specially in the case of high speeds of operation that the separate pieces of flat material are not suction-gripped by the suction openings of the separating roller, so that operation is not regular and sheets are not transported on every turn of the drum.
The cause for operation not being regular is that at very high speeds of separating there is not enough time for the leading edge of the furthest-forward piece of sheet material being moved up to be pulled from the keeping back drum, using the separating suction openings, over on to the separating drum. The operation of pulling over may furthermore be specially hard on processing specially stiff material to be transported.
The time in which the suction openings are able to take effect on the leading edge of the sheet material is, for this reason, less than the time needed by the leading edge for "jumping over" from the keeping back roller on to the separating drum.
In the case of the old apparatus it is lastly s shortcoming that the noise produced on separating the pieces of sheet material is generally loud, something which is more specially because the distance between the sheet material and the separating drum has to be crossed over very quickly at high speeds of operation of the apparatus, loud noises being produced by the sudden blowing or motion of air and the transported material being violently moved against a face of the apparatus.